A low-profile circularly polarized (CP) slot antenna to achieve a wide axial-ratio (AR) beamwidth is proposed in this paper. The radiating patch consists of two orthogonal pairs of parallel slots etched symmetrically onto a ground plane. Firstly, our theoretical study demonstrates that the CP radiation can be satisfactorily achieved at the broadside, when the vertical and horizontal paired-slots are excited in the same amplitude with 90° phase difference. Secondly, the principle of CP radiation of the proposed antenna on an infinite ground plane is described. Through analyzing the spacing between two parallel slots, the |Eθ| and |Eφ| radiation patterns can be made approximately identical with each other over a large angle range. As such, the slot antenna achieves a wide AR beamwidth. After that, the 3 dB AR beamwidth with respect to the size of a finite ground plane is investigated to constitute a practical CP antenna on a finite ground plane. In final, the proposed CP antenna with a 1–4 probe-to-microstrip feeding network is designed and fabricated on a finite ground plane of a dielectric substrate. Measured results are shown to be in good agreement with the simulated ones about the gain, reflection coefficient, AR bandwidth, and radiation patterns. Most importantly, a wide 3 dB AR beamwidth of 126° and low-profile property with the height of 0.036λ0 are achieved.

Triple band circularly polarized fractal boundary microstrip antenna is proposed and experimentally studied. The two orthogonal sides of the square patch are replaced with asymmetrical fractal curves for circular polarization (CP) radiation. A 45° rotated asymmetrical fractal slot is embedded at the center of the fractal patch for triband CP operation. The indentation factors of the fractal curves are optimized for better CP emission. The inserted fractal slot redistributes the current elements on the patch for triband CP radiation. The proposed antenna is implemented over a single layer with a single probe feed, so it is simple to fabricate and is cost effective when compared with the existing stacked layered multiband antennas in the open literature. The measured 3 dB axial ratio bandwidths of the proposed antenna at 2.4, 3.4, and 5.8 GHz are 2, 1, and 1.8%, respectively, so it is well suited for WLAN and Wi-MAX wireless applications.

By introducing a modified F-shaped feeding strip and dual parasitic shorted strips, a small-size wireless wide area network/long-term evolution (WWAN/LTE) printed antenna is proposed and embedded in the 4 G mobile phone with octa-band operation. The operating impedance bandwidths (RL ≥ 6 dB) of 263/1093 MHz can be obtained across the LTE/WWAN bands, respectively. The overall antenna size of the proposed printed monopole antenna (MA) is only 35 × 10 × 0.8 mm3. Meanwhile, this small-size MA provides the measured peak gains and antenna efficiencies of 2.0/3.6 dBi and 80/75% for the LTE/WWAN bands, respectively.

Aperture-coupled ESPAR antenna with a unique feed structure for switched beam application has been presented. The feed structure provides control over surface current of the driven element with the help of which main lobe can be steered in desired direction. This control has been achieved through the use of PIN-diodes. Finite element method has been utilized for design and simulated and measured results have been presented for validation. The antenna has the ability to steer the main beam in six directions. All radiation patterns are symmetric. The planar aperture-coupled nature of proposed antenna is ideal for integration and commercialization.

A single-layer coaxial-fed compact rectangular microstrip antenna with very low voltage standing wave ratio (VSWR) is presented in this paper. The simulated VSWR of the proposed antenna 1.00374 is obtained near the center frequency of the operating band (3.5 GHz). Simulation and measurement results indicate that the bandwidth (simulated: 3.36–3.715 GHz, and measured: 3.295–3.645 GHz) of the antenna exceeds 10% below VSWR 2, when the size reduction of the antenna is about 81.6%. The realized peak gain is obtained about 2.15 dBi at 3.5 GHz. For the verification of the computational results, two designs were fabricated and measured. Good agreements between simulated and measured results were found.

We report in this paper a novel miniaturized (12 × 18 × 1.6 mm3) microstrip fed UWB antenna with tunable notched band characteristics. The proposed antenna covers the tunable notched band for IEEE 802.11a wireless local area network operating in the frequency band of 5.15–5.825 GHz. The design of proposed antenna includes annular ring radiating patch with two T-shaped strips present inside it. The band notching is obtained by adjusting coupling between T-shaped strips placed inside the annular ring. In order to achieve larger bandwidth the ground plane of the microstrip antenna is modified. The simulated return loss of the proposed antenna has been verified in fabricated antenna experimentally, which has been in good agreement.

This paper presents a high gain, wideband circularly polarized (CP) antenna. High gain of the antenna is achieved by employing a frequency selective surface (FSS) as a reflector. The antenna is a coplanar waveguide-fed structure with a modified L-shaped radiating patch. The unit element of the FSS is formed by connecting two modified dipoles at an angle of 90°. The antenna with reflector has a measured impedance bandwidth of 74.3% (2.2–4.8 GHz) and a 3-dB axial ratio bandwidth (ARBW) of 62% (2.2–4.18 GHz). The maximum boresight gain of the proposed antenna with reflector is 7.1 dB at 3.4 GHz. The radiation patterns of the antenna with the FSS are also measured and compared with simulated patterns. The various aspects of effect of FSS on CP antenna performance are also discussed.

This paper presents a new broad band circularly polarized slot antenna array based on substrate-integrated waveguide (SIW) and aperture feeding techniques. The antenna element's impedance and 3 dB axial-ratio (AR) bandwidths are from 8.8 to 10.4 GHz (16.67%) and 9.5–10.7 GHz (12%), respectively. Employing aperture-coupled feed and combining this method with sequentially rotated network, a 2 × 2 antenna array is achieved. Parametric optimization procedure is used to enhance the antenna specifications. In the presented scheme by reducing mutual coupling caused by the SIW technique and sequentially rotated feed network, all parameters of antenna are improved. Consequently a novel antenna array with impedance bandwidth of 2.8 GHz (8.7–11.5 GHz) and 3 dB AR bandwidth of 2.1 GHz (9–11.05 GHz) are obtained. The average gain of the proposed antenna is about 16.7 dBic. A new method is used to increase the gain of antenna array. The extracted result shows that side lob level, mutual coupling, impedance bandwidth, and performance of antenna simultaneously are controlled.

A super-wideband (SWB) omnidirectional antenna is reported in Lau et al. in 2005 and 2008, but the antenna structure was complex and the radiation properties were unsatisfactory. In this paper, a SWB omnidirectional antenna with simple structure and improved radiation properties is presented. The antenna just consists of a two-stage inverted cone and two shorting pins. The proposed two-stage cone can improve the impedance matching in super-wide bandwidth, and the optimized shorting pins can reduce the cut-off frequency more than 50%. The calculated and measured results are investigated to confirm the antenna performances. The impedance bandwidth of the antenna for voltage standing wave ratio ≤ 2 achieves more than 1:22.1, covering 0.905 GHz to the above band. The smaller sizes than those referred by Lau et al. in 2008 are obtained. The profile of the antenna is 0.078λc, and the diameter of the radiation body is 0.217λc (λc is the wavelength of the cut-off frequency of the antenna). In addition, the radiation properties of the kind of SWB omnidirectional antenna are improved obviously. In the whole band, the ripple levels in horizontal radiation patterns are not more than 6.6 dB, and the cross-polarized levels are reduced by 9 dB.